The proposed project involves: the synthesis of certain key analogs as a test of a new structure-function model we recently proposed. The refinement of this model through further structural and biological studies; the continuation and development of proton and carbon-13 magnetic resonance studies of vitamin D-like substances, and the development of new synthetic routes to vitamin D analogs not involving photochemical steps. The general goals of the project include the development of an understanding of the mechanism of action of vitamin D and the synthesis of potentially useful analogs with high vitamin D or anti-vitamin D activity.